Mercenaries: If you battle in a clearing with two or fewer of your warriors, buy Mercenaries if any Riverfolk warriors are there.
If you want to place a building but you cannot place it anywhere, buy Mercenaries if it will let you place a building somewhere.
Vagabot: Exhaust one item for each service bought.
Pay with Riverfolk warriors.
You cannot buy mercenaries.
Automated Alliance: Pay with Riverfolk warriors
Logical Lizards: Never buy bird cards.